The present invention relates generally to diagnostic imaging and, more particularly, to a non-pixelated scintillator array incorporated into a detector array for a CT imaging system. More particularly, the invention relates to a scintillator array formed of a plurality of ceramic or single crystal fibers as well as a method and apparatus for forming the ceramic or single crystal scintillator fibers.
Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom.
Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator illuminates and thereby discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to the data processing system for image reconstruction.
Each photodiode of the photodiode array is aligned to correspond with a scintillator of the scintillator array. Known CT detectors have pixelated scintillator arrays that, ideally, are dimensionally equivalent throughout the scintillator array. Because there is a one-to-one relationship between photodiode and scintillator, it is imperative that each scintillator be precisely aligned with each photodiode. This precision becomes increasingly important as a result of the exactness required when developing reflector elements between the scintillator pixels and coupling a single-piece or multi-piece collimator assembly to the scintillator array. Because it is extremely difficult to form a small channel or groove between each pixelated structure, thicker reflector plates or walls are used to separate each of the scintillators. This leads to decreased surface area of the active scintillator and reduced quantum detection efficiency or dose usage. Reflector protecting material, such as tungsten, absorbs x-rays thereby increasing the radiation dosage required for data acquisition. Additionally, the specification for misalignment is usually very limited to maintain acceptable image quality. Further, high resolution applications require small scintillation cells which are difficult to form into a pixelated layout.
A number of fabrication techniques have been developed to achieve the necessary precision. These techniques include developing a ceramic wafer using well-known semiconductor fabrication processes and, through precisely controlled dicing and grinding, forming scintillator arrays or packs. Using accurate dicing and grinding processing and equipment, the packs may be processed to develop a series of pixelated structures. As noted above, however, the pixelated structures must be exactly aligned so that misalignment between the scintillators, photodiodes, and the collimator assembly during subsequent fabrication is minimized. Misalignment, however minor, can contribute to cross-talk, x-ray generated noise, and radiation damage to the photodiode array. If the misalignment is too severe, the scintillator pack must be discarded thereby increasing fabrication costs, labor, time, and waste.
Therefore, it would be desirable to design an apparatus and method of fabricating a scintillator array for high resolution CT imaging with reduced sensitivities to alignment of the scintillator array with the photodiode array and/or collimator assembly.